Portable communication devices such as cell phones are becoming increasingly pervasive as their costs have come down and their functionalities have increased. Throughout this Specification the terms “cell phone”, “cellular phone”, “mobile phone”, “smart phone” and “wireless phone” are used interchangeably. Such devices provide mobile users with the convenience to have voice calls from most locations using a number of standards such as code division multiple access (CDMA), Time division multiple access (TDMA), cellular second generation (2G), cellular third generation (3G), and cellular fourth generation (4G). Phone users with data plans can use their cell phone to send/receive email, check their calendar, browse the Internet, upload/download content, and store contact information and other data.
Other mobile devices such as personal digital assistant (PDA), laptop, tablet, digital/video camera, video game player, wireless headset, wireless mouse, wireless keyboard, pager, external hard drive, toy, electronic book reader, sensor, CD/DVD/cassette/MP-3 player, electronic appliance are also becoming popular. Throughout this Specification the term mobile device is used to apply to cellular phones as well as other mobile devices examples of which are given in this paragraph. Most mobile devices are now equipped with still image and video cameras and can take pictures and videos. High-end mobile devices are also computing devices that can download and run dedicated applications. Many mobile devices also support other wireless standards such as Near Field Communication (NFC), WLAN 802.11*(also called Wi-Fi), Wi-Fi Direct, Bluetooth®, Radio Frequency Identification (RFID), 60 GHz, and Ultra-wideband (UWB) standards.
Near Field Communication (NFC) is a short-range wireless technology that operates at 13.56 MHz and involves a reader (sometimes referred to as the “initiator”) and a tag (sometimes referred to as the “target”) that are in close proximity to each other; typically 10 cm or less. NFC typically transfers data at 106 kbps, 212 kbps, and 424 kbps. NFC tags store data in their memory that can be read by an NFC reader and displayed with an appropriate application such as a web browser, email client, etc. Tag capabilities vary depending on the size of their memory, communication speed, security, and data retention. The memory size is typically of the order of 512 bytes or less. The stored data can represent personal contacts, credit card information, personal identification numbers (PINs), rewards data, etc. The information stored in an NFC tag is usually read-only data that is provided by the manufacturer or encoded by the customer according to the NFC standard. Some tags however are rewritable.
Two NFC enabled devices have to be within a few centimeters of each other in order to communicate because NFC uses inductive coupling (also referred to as electromagnetic coupling) between the loop antennas of the NFC reader and the NFC tag. This short range reduces the possibility of malicious attacks and makes NFC ideal for electronic payment and ticketing applications. There are two main NFC communication modes; reader-writer NFC mode (also called the passive mode) and Peer-to-Peer (P2P) NFC mode (also called the active mode). In the reader-writer mode an NFC device reads an NFC tag or a device that is emulating a card. With this mode the reader provides an electromagnetic field and the tag responds by modulating and backscattering. Passive NFC tags communicate in this mode and therefore do not require batteries since they extract their power from the electromagnetic field of the reader. As a result, passive NFC tags can be low-cost tags, stickers and cards. In the P2P NFC mode two NFC devices create a connection to share some information. In this mode the reader and the tag each have their own power source and communicate in a P2P fashion, where each device generates its own field. In the P2P mode each device can also turn off its RF field (by turning off the power to its antenna circuits and coils) while the device is receiving or expecting to receive data. Active NFC tags operate in this mode and therefore require their own power, which results in more complexity and cost.
NFC offers some advantages over other short-range wireless communication standards, such as Bluetooth®. Unlike Bluetooth®, NFC does not require discovery, pairing, and menus. NFC also consumes less power than Bluetooth®, but operates at slower speeds. NFC devices just activate by close proximity. The simplicity and low-cost of NFC has potential for many applications. The NFC Forum was formed in 2004 and was charged with promoting NFC standards, applications, and devices. The NFC Forum has defined the NFC Data Exchange Format (NDEF) which is a binary format for storing and exchanging records of objects. These objects vary from Multipurpose Internet Mail Extensions (MIME) types to short documents such as uniform resource locators (URLs). For example, an NFC tag can hold a URL object that points to a server serving a document, business card, video, music, location, or map with location, etc. A shopper can place his/her NFC device near an NFC tag on a retail poster and receive coupons. A person can place his/her NFC device near an NFC tag and receive an audio or video presentation at a retail display or museum exhibit. A user can place his/her NFC device near the NFC device of another person to share a file, music, video, application, URL, business card, etc. An NFC device can touch a cashier's payment terminal and enter a pin to make a credit card type payment. NFC devices can also be used as ID cards that store personal information such as employment or medical data.
RFID is a tagging technology that uses radio waves to transfer information between RFID readers and RFID tags. The tags are typically attached to objects in order to identify and track them. RFID also operates in passive and active communication mode. RFID, however, has a greater range compared to NFC. The range of an RFID system depends on the frequency of its devices and the communication mode. In the active communication mode the tag has its own power source and the range can be from 10 centimeters up to 200 meters. In the passive communication mode the tag obtains its power from the RFID reader and the range of operation is a few meters.
The Bluetooth® standard provides short-range P2P connections between mobile devices. A Bluetooth® network is made up of small subnets or piconets. The latest standard is the Bluetooth® 4.0 standard which uses AES 128-bit encryption and claims speeds of 25 Mbps. The range of Bluetooth® is dependent on power and Bluetooth®-class and is typically of the order of 3 to 100 meters. Ultra-Wideband is another short range standard with a range of 10 to 20 meters.
Wi-Fi Direct is also a new standard from the Wi-Fi alliance that has a maximum range of over 200 meters and allows a mobile device to advertise itself as a combination of software access point and peer. Thus, a mobile device with Wi-Fi Direct can have a P2P connection to another mobile device while having a wireless LAN connection to an infrastructure network via an access point. The standard is easier to configure than previous ad-hoc methods and claims regular Wi-Fi speeds of up to 250 Mbps. It also provides security with WPA2 encryption and WPS (Wi-Fi Protection Setup) secure key handling. Wi-Fi Direct improves on the earlier WLAN 802.11 Ad-hoc by providing better interoperability and ease-of-use. IEEE 802.11z “Direct Link Setup” is also the 802.11 Working Group's take on improving ad hoc connections. The terms WLAN, 802.11 and Wi-Fi refer to the same set of wireless standards are used interchangeably in this Specification.
Another option for providing short-range communication is to use high frequencies. There are several standards bodies that are using high frequencies, such as 60 GHz. Examples of these include WirelessHD, WiGig, and Wi-Fi IEEE 802.11ad. Other short-range, high frequency standards are also supported by different mobile devices. In the U.S. the 60 GHz spectrum band can be used for unlicensed short-range data links (1.7 km) with data throughputs up to 2.5 Gbits/s. Higher frequencies such as the 60 GHz spectrum experience strong free space attenuation. The smaller wavelength of such high frequencies also enables the use of small high gain antennas with small beam widths. The combination of high attenuation and high directive antenna beams provides better frequency reuse so that the spectrum is used more efficiently for point-to-multipoint communications. For example, a larger number of directive antennas and users can be present in a given area without interfering with one another. Small beam width directive antennas also confine the electromagnetic waves to a smaller space and limit human exposure. The higher frequencies also provide more bandwidth and allow more information to be wirelessly transmitted.
Short-range Wi-Fi (or short-range 802.11) is another short-range communication method. For example a Wi-Fi access point can have two transmission powers; one for wireless connectivity and a lower power for position assistance data. The lower transmit power reduces the range so only nearby mobile devices receive data. Alternatively, the access point can use a higher frequency for transmitting the data. For example, the Wi-Fi and WiGig Alliances have agreed on a new Wi-Fi standard in the 60 GHz band for high speed (7 Gbps) short-range (about 10 meters) wireless communication. The previous two methods could also be implemented with the access point having a separate transceiver/communicator for short-range communication versus standard longer-range Wi-Fi connectivity.
Mobile devices use a number of different techniques that use wireless signals and process them into a location estimate. Typical information used for positioning includes Global Positioning System (GPS) signals, Received Signal Strength Indicator (RSSI), single trip or round-trip Time Of Arrival (TOA), Time Difference Of Arrival (TDOA), Angle Of Arrival (AOA), and Doppler shift. Triangulation is a common method where multiple range or angle measurements from known positions are used to calculate the position of a device. These techniques are complementary since some methods are more suited for indoor settings while others are more reliable in outdoor settings.
There are however a number of sources of errors in wireless positioning methods. One of the sources of errors is multipath propagation, which occurs when a signal takes different paths when propagating from a source to a destination receiver. While the signal is traveling objects get in the way and cause the signal to bounce in different directions before getting to the receiver. As a result, some of the signal are delayed and travel longer paths to the receiver. In other instances there is no direct line of sight because an object is completely blocking and any received signals occur only due to multipath propagation. Radio frequency (RF) signal amplitude is also greatly affected by metal objects, reflective surfaces, multipath, dead-spots, noise and interference. These effects cause errors in GPS data, RSSI, AOA, TOA, TDOA and Doppler shift. For example, time delays such as TOA and TDOA represent the longer multipath distance rather than the actual distance between the transmitter and the receiver. The longer multipath propagations also result in smaller signal amplitude indicators such as RSSI, as well as incorrect values for AOA and Doppler shifts. Other sources of positioning errors are clock drift, synchronization errors, and measurement errors. These errors cause incorrect mobile position calculations for traditional location techniques.